Travelling wave tube, in which an electron beam interacts with a helical delay line, having spurious oscillation suppressing means



lNvENToR AGENT Filed Feb. l, 1962 May 10, 1966 .1.A. B. DECHERING ETAL TRAVELLING WAVE TUBE IN WHICH AN ELECTRON BEAM INTERACTS WITH A HELICAL DELAY LINE, HAVING' SPURIOUS OSCILLATION SUPPRESSING MEANS United States Patent O 4 anims. (ci. sis-3.5)

The invention relates to a device having a travelling wave tube, in which the electron beam reciprocates with a helical delay line which at its ends is coupled to the -input and output conductor respectively which are connected together by a cylindrical wave guide which closely encloses the tube wall. The invention further relates to a travelling wave tube destined for such a device ln the devices of the above type yalready used, the problem presents itself that in the space between the helical delay line and the cylindrical wave guide which encloses the tube wall, parasitic modes of oscillation may occur. These may give rise to the generation of undesired oscillations. It is already known to provide in this space `damping material through a part of the length of the delay line in form of dissipating material which is provided -on a cylinder around the tube wall or as a thin metal or carbon layer on the inside or outside of the insulating tube wall.

Vlt is also known to provide for this purpose dissipating material on a dielectric cylinder which is located between the tube wall and the delay line and which encloses the latter substantially throughout the whole of its length. The drawback of the known means to yavoid undesired oscillations and feedback coupling between output and input wave guide is that in particular at the higher frequencies the oscillations are prevented in a limited frequency range only which decreases the usability of the plant.

The object of the invention is to provide a construction which has advantages with respect to the known constructions and which is composed in a simple manner. v

According to the invention, in a device of the type described above, a disc-shaped conductor is passed through the wall of the tube between the ends of the helical delay line, which conductor on the outside joins the Wall of the cylindrical wave guide which connects the input and output wave guide and in which this disc-shaped conductor is connected to a conductive tube which encloses the helical delay line with its insulating supporting rods closely and which tubular conductor extends over half to three fourths of the length of the delay line.

With the construction according to the invention, the feedback path between output and input Wave guides is restricted by the tube which encloses the helical conductor and as a result of its smaller diameter, the cut-oif frequency hereof is considerably higher than that of the cylindrical wave guide which encloses the wall of the tube. As a result of the high cut-off frequency it is not necessary to provide the conductive tube with damping material, since this tube will suppress parasitic modes of oscillation which may occur. Of course it is necessary that the connection of the leading-in disc to the Wave guide Wall provides a satisfactory high-frequency connection because otherwise feedback coupling might occur along this path.

In order that the invention may readily be carried into l effect, one embodiment thereof will now be described, by

Fatented May l, i966 way of example, with reference to the accompanying drawing, the sole ligure of which is a cross-section through the most important elements of part of the device according to the invention.

In the iigure, reference numeral It indicates the hollow input wave guide and reference numeral 2 the hollow output wave guide of an amplifier device having a travelling wave tube 3. Input and output wave guide are connected by a circular-cylindrical wave guide 4, Within which the glass wall S of the travelling Wave tube is located at a short distance. Two metal discs 6- and 7 respectively are sealed to the wall 5 which discs form the connection with the Wave guides 1 and 2 respectively. A short glass cylinder S is sealed to the other side of the disc 6, which cylinder comprises the parts of the electron gun not shown. The disc '7 supports, via a short glass cylinder, the collector electrode not shown. The helical delay line 9 is provided between the discs d and 7 by means of some transition parts, which line is supported by three ceramic rods l0. A third metal disc 11 is passed through the wall in the proximity of the disc 7, which disc 11 makes contact with the transition of the wave guides 2 and 4, in which a satisfactory tight highfre quency c-onnection is ensured. The disc 1l supports the satisfactorily conductive tube l2 consisting of coppernickel which extends through approximately two thirds of length of the delay line. The copper-nickel is not only satisfactorily conductive but also non-magnetic. With the exception of the damping material present on the helical delay line through part of its length, which material serves to avoid generating and is not shown, no damping means are present in or about the travelling Wave guide. Although the disc 11 is shown at the end of the tube 12, it may be provided, without objection, in the middle of the tube and may there also join the Wave guide 4.

What is claimed is:

il. A travelling-wave tube arrangement comprising an envelope, a rigidly supported helical delay line Within the envelope, input and output wave-guide means coupled to the respective ends of the helical delay line, a irst cylindrical wave-guide surrounding the envelope connecting the input and output wave-guides, a tubular conductor constituting a second cylindrical wave-.guide having a higher cutoif frequency than said first cylindrical wave-guide surrounding and extending about half to three-fourths of the length of the delay line, and a disc-shaped conductor between the ends of the helical delay line connecting the first and second cylindrical wave-guides for preventing feed-back coupling between the input and output waveguides.

2. A travelling-wave tube arrangement as claimed in claim 1 in which the second cylindrical Wave-guide is positioned within the envelope and is supported by the disc-shaped conductor which extends through the envelope.

3. A travelling-wave tube as claimed in claim 2 in which the helical delay line is supported by insulating support rods.

4. A travelling-wave tube as claimed in claim 2 in which the second cylindrical Wave-guide is a metal tube.

References Cited by the Examiner UNITED STATES PATENTS 2,857,547 10/1958 Klein et al S15-3.5

2,988,659 6/1961 Deimel S15-3.5 X

HERMAN KARL SAALBACH, Primary Examiner. GEORGE N. WESTBY, Examiner.

S. CHATMON, Assistant Examiner. 

1. A TRAVELLING-WAVE TUBE ARRANGEMENT COMPRISING AN ENVELOPE, A RIGIDLY SUPPORTED HELICAL DALAY LINE WITHIN THE ENVELOPE, INPUT AND OUTPUT WAVE-GUIDE MEANS COUPLED TO THE RESPECTIVE ENDS OF THE HELICAL DELAY LINE, A FIRST CYLINDRICAL WAVE-GUIDE SURROUNDING THE ENVELOPE CONNECTING THE INPUT AND OUTPUT WAVE-GUIDES, A TUBULAR CONDUCTOR CONSTITUTING A SECOND CYLINDRICAL WAVE-GUIDE HAVING A HIGHER CUT-OFF FREQUENCY THAN SAID FIRST CYLINDRICAL WAVE-GUIDE SURROUNDING AND EXTENDING ABOUT HALF TO THREE-FOURTHS OF THE LENGTH OF THE DELAY LINE, AND A DISC-SHAPED CONDUCTOR BETWEEN THE ENDS OF THE HELICAL DELAY LINE CONNECTING THE FIRST AND SECOND CYLINDRICAL WAVE-GUIDES FOR PREVENTING FEED-BACK COUPLING BETWEEN THE INPUT AND OUTPUT WAVEGUIDES. 